Re: [PATCH] utf8.c: fix strbuf_utf8_replace copying the last NUL to dst string

From: Junio C Hamano <gitster@pobox.com>
Date: Jul 29, 2014, 19:56 UTC
Message-ID: <xmqqha202b2v.fsf@gitster.dls.corp.google.com>
In-Reply-To: <1406639429-28748-1-git-send-email-pclouds@gmail.com>

Nguyễn Thái Ngọc Duy  <pclouds@gmail.com> writes:

> When utf8_width(&src) is called with *src == NULL (because the
> source string ends with an ansi sequence),

I am not sure what you mean by "because" here. Do you mean somebody (who?) decides to call the utf8_width() with NULL pointer stored in *src because of "ansi sequence"?

What do you mean by "ansi sequence"? I'll assume that you mean those terminal control that all use bytes with hi-bit clear.

At the very beginning of utf8_width(), *start can be cleared to point at a NULL pointer by pick_one_utf8_char() if the pointer that comes into utf8_width() originally points at an invalid UTF-8 string, but as far as I can see, ESC (or any bytes that would be used in those terminal control sequences like colors and cursor control) will simply be returned as a single byte, without going into error path that clears *start = NULL.

Puzzled...

> it returns 0 and steps
> 'src' by one.

Here "it" refers to utf8_width()?  Who steps 'src' by one?

Ahh, did you mean *src == NUL, i.e. "already at the end of the string"?

I think utf8_width() called with an empty string should not move the pointer past that end-of-string NUL in the first place. It makes me wonder if it would be a better fix to make it not to do that (and return 0), but if we declare it is the caller's fault, perhaps we may want to add

	if (!**start)
        	die("BUG: empty string to utf8_width()???");

at the very beginning of utf8_width(), even before it calls pick-one-utf8-char.

Still puzzled...

Show 8 quoted lines

> This stepping makes strbuf_utf8_replace add NUL to the
> destination string at the end of the loop. Check and break the loop
> early.
>
> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
> ---
>  utf8.c | 2 ++
>  1 file changed, 2 insertions(+)

Tests?

Show 13 quoted lines

> diff --git a/utf8.c b/utf8.c
> index b30790d..cd090a1 100644
> --- a/utf8.c
> +++ b/utf8.c
> @@ -381,6 +381,8 @@ void strbuf_utf8_replace(struct strbuf *sb_src, int pos, int width,
>  			src += n;
>  			dst += n;
>  		}
> +		if (src >= end)
> +			break;
>  
>  		old = src;
>  		n = utf8_width((const char**)&src, NULL);